The present invention relates to a process and device for the adjustment of rotational speed ratios between the operating elements of a draw frame. The rotational speed ratios are ruled and determined by the drive and the transmission in relation to the operating elements of the draw frame.
The operating elements of a draw frame are conventionally understood to be:
the roller pairs at the feeder frame, PA1 the roller pair at the feeder table preceding the draw frame PA1 the roller feeler pair used as a measuring element PA1 the pair of calender rollers following the draw frame PA1 the rotary plate PA1 the can plate PA1 compensate immediately and precisely for rotational speed ratio drops, PA1 render the basic rotational speed ratio continuously adjustable and fixable within relatively wide margins.
The listed operating elements are mentioned in a sequence which corresponds to their sequence in the direction of movement of the fiber sliver material. The most important elements in adjusting the rotational speed ratios on a draw frame are the roller pairs of the draw frame, i.e. the rotational speed ratios of the other operating elements are determined on the basis of the rotational speed ratio settings at these operating elements. The most important factor is the adjustment of the rotational speed ratio among the roller pairs of a draw frame.
The draw frames in most general use as a rule consist of several roller pairs between which the textile sliver is conveyed. It is characteristic that most draw frames have so many roller pairs that at least one preliminary drafting zone and one main drafting zone are formed. Each roller pair is driven by its lower roller. The draw frame is preceded by a roller feeler pair and is followed by a calender roller pair. The original form of the drive of the operating elements of a draw frame consisted of a main motor, with the rotational speed ratios of the different operating elements among each other being achieved by means of an intercalated gearing (used as a transmission). The rotational speed ratios between all the operating elements were thus rigidly set and could only be changed by replacing the replaceable rollers of the gearing.
A further development in the drive of the roller pairs of a draw frame, for example, is described in EP 376 002 for a draw frame with three roller pairs. Hereinafter, "drive" is understood to be the unit consisting of a motor and transmission. Due to differences in sliver thickness, the rotational speed ratio between central roller and delivery roller is changed, i.e. the main draft is changed and is thus adapted to the changed sliver thickness. The device has the decided disadvantage that interferences such as an electrical power outage or interference in the transmission between the main motor and the central rollers or input rollers result in a deviation in the subsequent rotational speed ratio between central roller and delivery roller. These interferences in the rotational speed ratios cannot be avoided. Load peaks of longer duration, e.g. at the input roller pair, caused by short thick places in the fiber material interfere with the synchronism of said rotational speed ratio because the feedback reactions do not have a uniform effect on all the roller pairs but are limited only to the central and input roller pair. Furthermore, it is disadvantageous that no position adjustment that would be true to the angle of rotation exists between delivery roller pair and central roller pair. This disadvantage becomes apparent when the draw frame is stopped. In stopping the draw frame, asynchronism in the rotational speed ratio between delivery roller pair occurs, caused by the inertia of the gearing which twists the central roller in relation to the delivery rollers. In today's draw frames which run at very high speeds, this situation takes on a great importance in affecting the length of fiber sliver produced per second.
Another development in the drive of draw frames is characterized by the utilization of an "electric shaft" in the draw frame. A characteristic solution for the utilization of the "electric shaft" is found in DE-OS 29 41 612. Each roller pair is driven directly by one single drive. There is no mechanical gearing between the roller pairs.
Based on the fundamental principle, the solution according to EP 411 379 proposes to unite similar individual drives into drive groups. Thus, separate drive groups which are independent of each other are provided. An individual drive is to be provided for each independent drive group of a drafting zone, or as required also of a conveying or transportation segment or any other operating stations connected in the process. The "electric shaft" principle is maintained. The precision of the drives is to be improved by using position adjusters which are true to angles of rotation. It is a disadvantage here that the servomotors must possess a high electric capacity and great precision in rotational speed and are very expensive for that reason.
The technical solution according to EP 411 379 advantageously eases the load of the central computer by means of a subdivision into a main and at least one auxiliary control and reduces the danger of high surges occurring in the main controls (EP 411 379, column 5, lines 27-31). This solution cannot, however, prevent the drive motors of the different drive groups from deviating in rotational speed ratio among each other. This may be caused by suddenly occurring errors in the textile fiber sliver, for instance. EP 411 379 therefore proposes to install control connections between the auxiliary controls in order to detect deviations in the rotational speed ratio of individual drive motors among each other and to correct such deviations.
The solution according to EP 411 379 is finally very costly and expensive since every individual drive must function very precisely. If the necessary mechanical performance to be furnished and the size of the motors and of their electronic elements are taken into account it clearly appears that additional problems of space requirement and air-conditioning of the electronic elements in keeping with the size of the spinning room exist. Considering the dynamic aspects of the individual drives, it is clear that when load changes occur suddenly or in case of load peaks, e.g. due to the entry of thick places in the fiber sliver, it becomes very difficult or is in part or entirely impossible to maintain precise rotational speed ratios or to prevent brief rotational speed collapses due to momentary peaks. To be able to compensate these rotational-speed collapses rapidly and effectively with the necessary torque, the electric drive motors are generally over-sized with respect to their capacity requirements.
Individual drives with this "electric shaft" have furthermore the disadvantage with respect to adjustment that desired-value deviations are of different importance. The correction of small deviations in the desired value requires the utilization of an expensive servo-adjuster by contrast to the correction of great deviations in the desired value.
The achievement of a basic draft, e.g. 8 times, requires a rotational speed ratio of 800% between two draw-frame shafts. The desired value of the voltage changer of the slow motor is therefore only 1/8 of the desired value of the guiding drive. To ensure that the adjustment precision is not considerably impaired in this case, an expensive drive of much higher precision (8 times) than inexpensive standard drives must be used.
The following situation is also disadvantageous:
Changes in percentage of drafting result in a modification of the setting signal, i.e. a fine draft has a very weak setting signal as a result. This is a problem, as the precision of synchronization of the rotational speed ratios suffers when very low signal magnitudes are used for the setting signal.